1. Field of the Invention
This invention relates generally to a new polymer material, and, more specifically, to a new polymer material that has excellent oxidative stability up to about 5V (vs Li/Li+), making it suitable for use in high voltage electrochemical cells.
Conventionally, cathodes for lithium battery cells are made up of particles of cathode active material, bound together by polyvinylidene fluoride (PVDF). PVDF can also be used in anodes to bind together particles of anode active material. PVDF is electrochemically stable in contact with a wide variety of electrolytes and is oxidatively stable up to about 5.0 V (vs Li/Li+O.
Unfortunately, PVDF acts only as a binder in the cell. It is functionally inert and adds dead weight and volume. In addition, PVDF has a glass transition temperature (Tg) of about −35° C. and a melting temperature (Tm) of 160° C., so it is very hard at typical cell operating temperatures.
As rechargeable batteries find more and more applications, energy density and power density are critical. In an ideal situation, a cell would include no dead weight, i.e., it would contain only those elements that have electrochemical functions in the cell.
It would be very useful to find a binder material for use in cathodes and anodes, which can also provide some electrochemical function, thus increasing the energy density and/or power density of the cell. Another useful improvement would be for a binder to have some flexibility so that it can be resistant to fracture during cell use and thereby have a long lifetime.